This invention relates to a slip-controlled brake system provided for road vehicles where one front wheel and one rear wheel at a time are connected to a common braking pressure control channel and where the individual wheels are equipped with sensors for the detection of the rotational behavior of the wheels. Braking pressure modulators are controllable by the signals of the sensors after the handling, logical combination, and processing of the signals, with the rotational behavior of the individual wheels influencing the braking pressure variation in the braking pressure control channels as a function of predetermined selection criteria such as "select-low" and "select-high" criteria and on additional conditions, in particular on limit values. This invention further relates to brake systems in general which are equipped with braking pressure modulators, by means of which the braking pressure at the individual wheels may be varied individually or in groups, and which have wheel sensors. The braking pressure modulators are controllable by the signals of said sensors after the handling, logical combination, and processing of said signals by means of electric circuits comprising a cornering identification circuit.
For the sake of simplifying slip-controlled brake systems and for the sake of rendering them cheaper known systems provide but one or two braking pressure control channels instead of individual control of all wheels. In order to nevertheless avoid lock-up of the wheels connected to one common channel according to the "select-low" principle the wheel with the strongest deceleration is used for governing the braking pressure. In so doing, and with respect to the second wheel controlled along with the first one, one does not utilize the adhesive value to the maximum extent possible. As a result thereof the length of the necessary stopping distance may increase. If, on the other side, slip control depends on the "select-high" principle (i.e., on the faster wheel or rather on the wheel decelerated less) in many cases it is impossible to avoid excessive slip or even a lock-up of the wheel controlled along with the first one.
It is also known to abandon a fixed coordination of the wheels with a certain control group governed either by the "select-low" principle or by the "select-high" principle. Instead, in a known anti-skid system (European Patent=E.P.-A-51801) at first one determines which wheel has the worst road surface contact, ignoring its rotational behavior and controlling all the other wheels jointly according to the "select-low" criterium. In the case of a dual-circuit brake sytem with diagonal split-up, in this known system the circuit with the wheel, which is the first to become unstable, is switched to "select-high" control, the other circuit being switched to "select-low" control. This method is disadvantageous in that in some situations (e.g., when changing lanes or in a bend) there may result excessive debraking. It is therefore an object of this invention to overcome the mentioned disadvantages of the known brake systems and to provide a slip-controlled brake system which despite the limitation to two braking pressure control channels ensures a safe braking action with a short stopping distance even in unfavorable situations and in particular when braking in a bend or when changing lanes.
Generally, this invention adapts the controlled braking pressure variation to the varying conditions and physical factors of straight-onward driving and of cornering such as to maintain the driving stability and steerability as far as possible in all situations.